This invention relates to sphygmomanometers and other devices.
It is a well-known medical and veterinary diagnostic procedure to use a sphygmomanometer to obtain a measure of the hydrostatic pressure under which blood exists in the arteries and veins of human beings and animals. The most common sphygmomanometer comprises (a) a bag or bladder forming or contained in a cuff, the bladder being inflatable with air by a hand bulb communicating with the bladder via a one-way relief or regulator valve, and (b) a pressure guage or like pressure measuring instrument that communicates with the air inside the bag and provides a measure of the pressure (and that is generally expressed in mm of mercury).
In the auscultation method for obtaining a measure of blood pressure, the bladder or bag is wrapped around the subject""s arm (usually the left arm) above the elbow in a position appropriate to shut off blood flow in the brachial arteryxe2x80x94the principal artery of the upper armxe2x80x94when the bag is inflated. Utilising the hand bulb, air is pumped into the bag until the subject""s pulse in the brachial artery disappears. This is noted by the clinician (i.e. doctor, nurse or other operator) listening via a stethoscope placed over the brachial artery in the vicinity of, (e.g. just below) the elbow, for the faint tapping sounds corresponding to the heartbeat. After effective closure of the brachial artery, the air pressure within the bladder is then allowed to decrease slowly via the one-way relief valve whilst the clinician listens, via the stethoscope, for the first onset of the faint tapping sounds corresponding to the heartbeat to re-appear. The reading of the guage at this moment gives the systolic blood pressure, i.e. the pressure necessary to suppress the maximum pressure of blood in the artery. The air pressure within the bladder is then further decreased slowly, via the one-way relief valve, whilst the pulse beat is monitored. As the air pressure compressing the artery is diminished, the sounds become progressively louder and eventually change in quality from loud to soft before they ultimately disappear. This corresponds to the pressure at which the maximum pulse wave is (again) obtained and marks the diastolic blood pressure, i.e. the pressure when the heart is in diastole with arterial pressure at its minimum.
Recent studies, notably by the British Hypertension Society and Professor O""Brien of Beaumont Hospital, Dublin (Ireland), suggest that the accuracy of the results of blood pressure measurement can be assured (a) if there is no overlap of the ends of the inflatable bladder and (b) if the inflated bladder extends around as near as possible to 100% of the subject""s arm, preferably at least 80% of the circumference of the subject""s arm.
It will be appreciated that achieving such desiderata is extremely difficult in practice due to the considerable arm size variations between different people. Further difficulties arise due to the varying degrees of taper of the upper arm from one person to another.
One previously-proposed solution is to provide a range of differently sized cuffs and select one to fit the patient whose blood pressure is to be measured. This is time consuming and in a clinic or hospital, requires increased stock levels of the differently-sized cuffs.
Another previously-proposed solution is to provide a single external cuff which houses therein three separate bladders of different length (and width) dimension, only the bladder of the requisite size being inflated in use. This cuff is a multi-layered structure prone to leakage or failure and is also an expensive item.
Another, and not necessarily related, field concerns ratchet mechanisms and in particular to ratchet mechanisms involving relative arcuate movement between the ratcheting parts.
It is a well-known to provide a rotary ratchet mechanism in which the ratchet and pawl may be disengaged by depressing a button in a generally radial direction to deflect the pawl out of enagagement of the ratchet teeth. Where the rotary ratchet mechanism has no spring or like resilient means to effect counter-rotation when the ratchet and pawl are disengaged, the disengagement procedure is generally an inconvenient two-handed operation requiring one hand to effect rotation or counter-rotation of the rotary member of the ratchet mechanism and the other hand to effect depression of the disengagement button.
It is therefore considered desirable to overcome or at least minimise one or more of the aforesaid and/or other difficulties.
According to a first aspect of this invention there is provided, for a sphygmomanometer, cuff means comprising an inflatable cuff having a length susceptible to inflation, and constriction means to constrict the cuff at different positions along it thereby to vary the said length from a maximum to an effective length less than the maximum.
According to a second aspect of this invention there is provided, for a sphygmomanometer, cuff means comprising an inflatable cuff having a length susceptible to inflation, and constriction means relatively moveable with respect to the cuff and thereby to constrict the cuff at different positions along it whereby the said length can be varied from a maximum to a desired effective length less than the maximum.
Advantageously the constriction means is operable to vary said length continuously such as to select or pre-set any desired effective length for the cuff (preferably in the range of about 20% to 100% of the maximum length).
Preferably the cuff means comprises a housing, a spindle rotatable therein to which one end of the inflatable cuff is attached, an opening in the housing through which the inflatable cuff may extend, and an end unit to which the other end of the inflatable cuff is attached, said end unit being in use releasably fastened to the housing such that a desired effective length of cuff can be withdrawn from the housing via said opening to extend in a loop around the upper arm of a patient.
The remaining portion of the cuff wound around the spindle within the housing is constricted against inflation by such winding and/or by its engagement of the opening. In this regard it will be appreciated that, being a pressure application device, small differences in the effective length of the cuff (providing the external loop) are unlikely to have a material significance. It is this loop which in use extends around the upper arm of the subject whose blood pressure is to be taken (i.e. measured).
In one preferred embodiment the opening is provided by a slot formed between two co-operating parts of the housing.
Advantageously the end unit and the housing are provided with mutually co-operable snap-fastening attachment means.
Preferably, releasable fastening meansxe2x80x94to fasten said end unit releasably to the housingxe2x80x94is attached to one or other of the end unit and housing in a manner permitting their relative twisting. This permits the portion of the cuff that extends between the end unit and the housingxe2x80x94and which in use forms a loop around the patient""s upper armxe2x80x94to accommodate the tapering nature of the patient""s upper arm.
Preferably the degree of permitted angular twisting is in the range 5xc2x0 to 15xc2x0.
According to a third aspect of this invention there is provided, for a sphygmomanometer, cuff means comprising an inflatable cuff having a length susceptible to inflation, and means permitting the cuff, in use, to adopt a frusto-conical form to accomodate the taper of a subject""s limb, e.g. the upper arm of a human patient.
According to a fourth aspect of this invention there is, provided, for a sphygmomanometer, cuff means comprising an inflatable cuff having a length susceptible to inflation, and fastening means comprising first and second mutually interengageable parts spaced apart longitudinally of the cuff, one of said parts being attached to the cuff by means permitting the fastened cuff, in use, to adopt a frusto-conical form.
By permitting the fastened cuff, in use, to adopt a frusto-conical form, varying degrees of taper of the upper arm can be accomodated thus allowing cuff use for a wide range of people with different arm sizes and tapers.
Preferably the cuff means comprises a ratchet mechanism to restrain withdrawal of the cuff from the housing, and release means operable to permit such withdrawal.
Advantageously said releasable ratchet mechanism is one-hand operable and comprises a rotatable input member (e.g. a knob unit) and a rotatable output member (e.g. a spindle, preferably coaxial with the rotatable input member), rotation of the input member in a first direction effecting rotation of the output member in that direction but preventing rotation of the output member in a second, opposite direction, and rotation of the input member in the opposite second direction permitting rotation of the output member in that second direction.
Preferably this is achieved by providing first and second mutually engageable ratchet means that, when the input member is rotated in said first direction are in mutual cooperative engagement to prevent said rotation of the output member in the second direction, and that are disengaged when the input member is rotated in the said opposite, second directionxe2x80x94to permit said rotation of the output member in the second direction.
According to a fifth aspect of this invention there is provided a releasable ratchet mechanism that is one-hand operable and comprises a rotatable input member, a rotatable output member, and mutually engageable ratchet means effecting selectively disengageable coupling between the said input and output members such that rotation of the input member in a first direction effects rotation of the output member in that direction but prevents rotation of the output member in a second, opposite direction, and such that rotation of the input member in the opposite second direction permits rotation of the output member in that second direction.
Preferably the ratchet mechanism comprises first and second mutually engageable ratchet means that, when the input member is rotated in said first direction, are in mutual co-operative engagement to prevent said rotation of the output member in the second direction and that are disengaged when the input member is rotated in the said opposite, second directionxe2x80x94to permit said rotation of the output member in the second direction.
Advantageously, the mechanism comprises a pawl fast with one member (preferably the output member) for extension through a slot in the other member (preferably the input member) and to engage an arcuate array of fixed ratchet teeth, one of the bounding edges of said slot deflecting the pawl inwardly when the other member is rotated in said second direction.